Magnetic resonance imaging of blood–brain barrier permeability in ischemic stroke using diffusion-weighted arterial spin labeling in rats

Diffusion-weighted arterial spin labeling magnetic resonance imaging has recently been proposed to quantify the rate of water exchange (K_w) across the blood–brain barrier in humans. This study aimed to evaluate the blood–brain barrier disruption in transient (60 min) ischemic stroke using K_w magnetic resonance imaging with cross-validation by dynamic contrast-enhanced magnetic resonance imaging and Evans blue histology in the same rats. The major findings were: (i) at 90 min after stroke (30 min after reperfusion), group K_w magnetic resonance imaging data showed no significant blood–brain barrier permeability changes, although a few animals showed slightly abnormal K_w. Dynamic contrast-enhanced magnetic resonance imaging confirmed this finding in the same animals. (ii) At two days after stroke, K_w magnetic resonance imaging revealed significant blood–brain barrier disruption. Regions with abnormal K_w showed substantial overlap with regions of hyperintense T₂ (vasogenic edema) and hyperperfusion. Dynamic contrast-enhanced magnetic resonance imaging and Evans blue histology confirmed these findings in the same animals. The K_w values in the normal contralesional hemisphere and the ipsilesional ischemic core two days after stroke were: 363 ± 17 and 261 ± 18 min⁻¹, respectively (P < 0.05, n = 9). K_w magnetic resonance imaging is sensitive to blood–brain barrier permeability changes in stroke, consistent with dynamic contrast-enhanced magnetic resonance imaging and Evans blue extravasation. K_w magnetic resonance imaging offers advantages over existing techniques because contrast agent is not needed and repeated measurements can be made for longitudinal monitoring or averaging.